1. Field of the Invention
This invention relates generally to equipment for pools and particularly relates to a drain cover for swimming pools and the like.
2. Description of the Prior Art
Swimming pools require a suitable outlet for drawing water from the pool for recirculation and purification. This outlet (the "main drain") is customarily recessed at the low point in the pool and requires a perforated cover or grate to keep larger objects from clogging the outlet. Swimmers must also be kept away from the outlet since the pump suction may hold them underwater until they drown. For this purpose many drain grates and the like have been developed in the past. However, most of the drain grates consist of a substantially flat cover for the main drain. This cover plate is perforated or provided with annular drainage rings. Thus the rings of the cover may be interconnected by radially extending spokes.
Such a construction presents various hazards to the user of the pool. In the first place, there is considerable suction at the cover, even though it is displaced from the outlet pipe opening proper. Hence, it is possible for a swimmer who might rest momentarily with his back or chest on such a drain cover to be prevented from getting up again by the strong suction of the water, and may still result in drowning. In some drain covers, the openings may be large enough for a child's finger to get caught, again possibly resulting in drowning. Other drain covers, while avoiding the grate pattern, incorporate a lip or ledge extending upward from the bottom of the pool, thus causing a swimmer to stub his toes.
Still another problem with prior art drain covers is that they are subject to failure from certain applied loads, such as a swimmer pushing up from the bottom of the swimming pool or jumping into the pool feet first from the edge or from a diving board, especially in the case of shallow pools for small children. Such loads may cause damage and may fracture the cover which may again, result in accidents.
Some of the prior art drain grates have been made of metal. In that case, the Uniform Swimming Pool Code, promulgated by the International Association of Plumbing and Mechanical Officials, requires that such a metal cover be electrically grounded to prevent possibility of electrical shock to a swimmer. Thus a plastic drain cover solves the problem without the need for grounding.
Other prior art drain covers have featured a directional-flow inlet or the like which may cause a vortex to form. This is undesirable since it also develops a tendency to trap a swimmer under water.
Recent regulations in code specifications for swimming pools, therapy pools, hot tubs, saunas and the like require that a design for drain covers cannot be approved unless actual full-size units pass several tests, performed by a licensed testing laboratory. These tests include a progressive static load test, an impact test where a load is dropped onto the center of the cover, and a flow restriction test. The total area of all openings associated with the drain cover permitting flow from the pool into the drain beneath the drain cover must be sufficient to avoid restricting the flow appropriate to the specific drain size for which it is intended. Some codes restrict the maximum size of openings to five-eighths, or even one-half, inch to prevent fingers and toes from entering. Also, specified for some codes is the requirement that these holes be arranged and located such that they cannot be covered (closed) by any part of the body, including hands and feet. These requirements and restrictions tend to direct that complaint drain covers will have some part of the cover spaced away from the surface in which the drain is located in order to keep the flow passages clear. This also causes the drain cover to become a possible hazard to toe stubbing or to impact with other body parts subject to encounter as a swimmer is skimming along the bottom of the pool.